When nine out of ten staff report that they "make a difference" on a daily basis, they are surely part of a highly motivated and dedicated workforce, working for an effective organisation.

That organisation is the NHS, for which three out of four staff regularly work extra hours without pay. These results are from the latest NHS staff survey. Not only have they barely changed between 2010 and 2011, they also match the still high levels of public satisfaction with the NHS. Perhaps both indicators are a product of the huge expansion of health spending under Labour from 2001 onwards.

But what happens now that the health and social care bill is becoming law? Over the next few years some of those staff will cease to work for the NHS; the trusts for which some work will expand their private income; competition and fragmentation may reshape trusts and service lines. How far does that sense of making a difference to patients stem from being part of the loose and baggy monster that is the NHS and how far does it come from working in healthcare, regardless of its superstructure?

Like all surveys, this annual test of staff opinion is limited in its reliability. The survey sample may tend to pick up both the more critical and the more enthusiastic. A lot of NHS staff, those who didn't respond, may be as indifferent as the workforce at large.

The survey results are broken down to individual trust level , but this raises difficulties. Because most trusts and regulators such as Monitor and the Care Quality Commission use findings in their appraisal of NHS trusts, trusts have an incentive to boost results, encourage responses, preferably of a positive kind.

That's because staff do think their work matters but are often critical of the particular NHS provider or commissioning body employing them. Only half recommend their own trust as a place to work; only a third feel their trust values their work. A telling figure for the NHS is the proportion who don't think their hospital or facilities are good enough to entrust the care of their relatives to – 11% said they would be unhappy with the standard of care provided. Is that high? How many bankers would recommend you trust your money to their firm? How many Tesco staff would (under the cover of anonymity) recommend that company's stores?

Turn the glass the other way round: nearly 90% of staff would entrust a relative to their colleagues' care or have no view either way. That could sound like a ringing endorsement.

The headline figures are intriguing rather than explanatory. If four fifths of NHS staff are satisfied with the quality of care offered patients, only two thirds feel they are able to do their job "to a standard they are personally pleased with". The same proportion think there is not enough staff for them to do their job properly.

The survey also reminds us that while the public may say they love the NHS that doesn't stop individuals treating NHS staff badly. One in 12 report physical violence from patients, relatives or other members of the public, and one in six bullying or harassment from those they are seeking to help.